Method and apparatus for two-part CMP retaining ring

ABSTRACT

A two piece retaining ring used for chemical mechanical polishing of semiconductor substrates comprising a relatively rigid upper portion and a less rigid lower portion. The two pieces of the ring are secured to each other by snapping a central channel and extending arms over a central neck extension of the upper part.

FIELD OF INVENTION

This invention relates to a two part retaining ring typically used in chemical mechanical polishing operations.

BACKGROUND

The present invention relates to a retaining ring used in the process of chemical mechanical polishing of semiconductor substrates. The substrate is typically a thin disc of semiconductor material with deposited alternate layers of conductive, semiconductive, and insulating materials. The layers are etched to produce electrical circuitry on the surface of the substrate. A typical substrate has a series of layers deposited and circuitry etched. The deposition and etching process after many layers produces a non flat top surface. This unflatness prevents accurate deposition of subsequent layers. Planarization of the substrate is periodically required to maintain an acceptable substrate surface. Chemical mechanical polishing of the topmost surface of the substrate produces a sufficiently flat surface to allow accurate subsequent deposition and etching of layers. This method of planarization is affected on a substrate by use of a polishing machine. Among the many subassemblies of this machine is the polishing head or carrier head. The polishing head contains among its components a retaining ring. This ring positions and retains the substrate allowing the other components of the head to exert pressure against the substrate which in turn moves relative to a polishing pad, usually wetted by a polishing medium or slurry.

The retaining ring is typically composed of two pieces. The first, or upper, piece is usually of a metal material such as stainless steel, aluminum, or molybdenum, but may be other materials. The second, or lower, piece is of a plastic material such as polyphenylene sulfide (PPS), polyethylene terephthalate, polyetheretherketone, polybutylene terephthalate or Ertalyte TX from Quadrant Engineering Plastic Products.

U.S. Pat. No. 6,251,215 to Zuniga describes a two part chemical mechanical polishing (CMP) retaining ring where the first part is polyphenylene sulfide (PPS) and the second part is metal and the parts are joined by an epoxy adhesive. The '215 patent references, but does not describe, mating the first piece to the second piece by a plurality of individual screws.

U.S. Pat. No. 6,186,880 to Gonzalez et al describes a recyclable retaining ring assembly comprising a plastic wear ring portion with a raised neck 38 which is inserted into an opposing channel or groove 36 of a metal backing ring 34.

U.S. Pat. No. 6,089,960 to Messer describes the use of one or more elastomeric shim rings in the CMP head.

The plastic portion of the ring is in physical contact with a polishing pad and slurry. Over a certain period of time the exposed surface of the ring is worn down due to the abrasiveness of the pad and slurry. Eventually the ring is no longer functional and must be replaced.

It is desirable to provide a method of replacing the plastic wear portion of the two part ring. In some embodiments, the replacement of the plastic wear portion may be conducted at a customer site so that shipping cost can be reduced. Alternately, the entire ring may be shipped back to a supplier for rework, where the plastic wear portion would be replaced.

SUMMARY

The invention is directed toward a method of fastening together two parts of a retaining ring used in the chemical mechanical polishing process of a semiconductor substrate. The first, or upper, part is typically a metal material such as stainless steel, aluminum, or molybdenum. The second, or lower, part is of a plastic material such as PPS.

One embodiment of the present invention is a plastic ring which has inner and outer peripheral snap features to snap onto the metal backup ring. In one embodiment, the snap features include a lip projection which engages a peripheral slot in a neck extension in a metal backup ring.

The present invention permits less expensive replacement rings, and faster maintenance relative to prior art retaining rings.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of the present invention are set forth below and further made clear by reference to the drawings, wherein:

FIG. 1A is a top view of a retaining ring.

FIG. 1B is a side view of the retaining ring of FIG 1A.

FIG. 2 is an exploded top perspective view of a retaining ring.

FIG. 3 is a cross section view A-A of the ring of FIG. 1

FIG. 4 is a cross section view B-B of the ring of FIG. 1

FIG. 5 is a detailed cross section view of the upper part of the ring of FIG. 1

FIG. 6 is a detailed cross section view of the upper part of the ring of FIG. 1

FIG. 7 is an exploded perspective view of an assembly fixture for snapping the lower part of the ring onto the upper part of the ring.

DETAILED DESCRIPTION OF EMBODIMENT—Lower Part Snapping onto Upper Part

Referring to FIG. 1A which is a top view of a retaining ring 100, the ring includes an upper part 150 and a lower part 200 (not shown). Both the upper part and the lower part are annular rings. The retaining ring 150 is typically mounted to a carrier head (not shown) by screws 110 along the top surface of the upper part.

FIG. 1B is a side view of the retaining ring of FIG. 1A, which shows the lower part of the ring 200 covering the outside edge of the upper part 150 (shown by hidden line). The lower part may include a gap which facilitates expanding the plastic portion slightly to fit over the upper portion. In this embodiment, the lower part is snapped onto the upper part.

Referring now to FIG. 2 which is an exploded top perspective view of a retaining ring, the two piece retaining ring 100 is composed of two parts, the first or upper part 150 is typically made of a metal, and the second or lower part 200 is typically made of plastic such as, polyphenylene sulfide (PPS), polyethylene terephthalate, polyetheretherketone, polybutylene terephthalate or Ertalyte TX. The lower part includes a central annular channel 250 which receives an extended neck portion (not shown) of the upper part.

Referring now to FIGS. 3 and 4 which are cross section views of the assembled part and to FIGS. 5 and 6 which are detailed cross section views of the upper and lower parts respectively, the upper part 150 includes a downwardly extending annular central neck portion 160 which cover substantially all of the width of the upper part. The downwardly extending annular central neck portion is received in the central annular channel 250 of the lower part. The downwardly extending annular central neck portion has a first wall surface 162 toward the center of the retaining ring and a second wall surface 172 away from the center of the retaining ring. There is a first annular inset 164 in the upper portion of the first wall surface 162, and a second annular inset 174 in the upper portion of the first wall surface 172.

The central annular channel 250 includes an upper mating surface 255, an inside wall 260 toward the center of the retaining ring extending upwardly from the upper mating surface, and an outside wall 270 away from the center of the retaining ring extending upwardly from the upper mating surface. The inside wall has a third wall surface 260 which may include a first lip 262 which engages the first annular inset 164, and the outside wall has a fourth wall surface 270 which may include a second lip 272 which engages the first annular inset 174.

The upper part may include at least one hole 180 for receiving a pins 190. The hole typically extends 210 partially through the lower part 200 so that the pin prevents a rotation of the lower part relative to the upper part.

The neck portion 160 and the central annular channel 250 may include radiused comers as shown by 165, 175, 264, and 274. In one embodiment, the inside wall 162 of the neck portion 160 is perpendicular to the top mounting surface 152 of the upper part. In another embodiment, the inside wall 162 has a slight taper, such as about 2 degrees toward the outside of the ring as shown in FIG. 5B. This taper typically begins below the first inset 164.

In one embodiment, the first material is stainless steel and the second material is polyphenylene sulfide which includes TechTron® by DSM, Quadrant Engineering Plastic Products, Ryton® by Chevron-Phillips, and by Ensinger Corporation. In other embodiments, the second piece is a plastic material such as, polyethylene terephthalate, polyetheretherketone, polybutylene terephthalate or Ertalyte TX.

DETAILED DESCRIPTION OF EMBODIMENT—Detailed Dimensions

In one embodiment, the first wall has a thickness of about 0.108 inches and a height of about 0.250 inches; the first lip has a height of about 0.023 inches and has an extension of about 0.005 inches; the second wall has a thickness of about 0.085 inches and a height of about 0.690 inches; and the second lip has a height of about 0.039 inches and has an extension of about 0.008 inches.

DETAILED DESCRIPTION OF EMBODIMENT—Vibration Isolation

In this embodiment, a vibration isolation element, such as an o-ring or RTV sealant is employed between the lower part wear portion of the ring and the upper part backing portion of the ring.

DETAILED DESCRIPTION OF EMBODIMENT—Fixture

Referring now to FIG. 7 which is an exploded perspective view of an assembly fixture for snapping the lower part onto the upper part, the fixture 400 includes an upper plate 410 and a lower plate 420. Dowels pins 430-433 are inserted into the lower plate and through corresponding holes 440-443 in the upper plate. The dowel pins include springs 450-453. The lower plate 420 includes a recess 460 for receiving the bottom part of the retaining ring. An O-ring 470 may be placed in a portion of the recess 460.

For assembly, the lower part is placed into the recess 460 of the lower plate 420 which has the dowel pins and springs in place as shown in FIG. 7. The upper part is placed over the lower part, and the upper plate is inserted over the dowel pins. The upper plate is then forced downward, thereby pushing the neck extension of the upper part into the central annular channel of the lower part.

In order to remove a lower plastic part from the upper part, long screws may be inserted through the twelve mounting holes 110 in the upper part in order to break off the used lower part. 

1. A retaining ring for a carrier head, the retaining ring comprising: a first rigid annular portion comprising a downwardly extending annular central neck portion; a second annular portion of a less rigid material than the first portion, the second portion comprising a central upwardly facing channel; and a snap connection means such that the central upwardly facing channel of the second annular portion may be snapped over the downwardly extending annular central neck portion of the first rigid annular portion.
 2. The retaining ring of claim 1 further comprising a rotation prevention means which prevents the second annular portion from rotating with respect to the first rigid annular portion.
 3. The retaining ring of claim 1 further comprising a vibration reduction means between the second annular portion and the first rigid annular portion.
 4. The retaining ring of claim 1 wherein the snap connection means is at least one lip on the second annular portion which fits into an annular slot on the first rigid annular portion.
 5. A retaining ring for a carrier head, the retaining ring comprising: a first rigid annular portion comprising a downwardly extending annular central neck portion having a first wall surface toward the center of the retaining ring and a second wall surface away from the center of the retaining ring, a first annular inset in the upper portion of the first wall surface, and a second annular inset in the upper portion of the second wall surface; and a second annular portion of a less rigid material than the first portion, the second portion comprising a central upwardly facing channel having a third wall toward the center of the retaining ring and a fourth wall away from the center of the retaining ring, a first lip in the upper portion of the third wall, and a second lip in the upper portion of the fourth wall, such that the downwardly extending annular central neck portion of the first rigid annular portion nests in the central upwardly facing channel of the second annular portion, and the first lip engages the first annular inset, and such that the second lip engages the second annular inset.
 6. A retaining ring for a carrier head, the retaining ring comprising: a first rigid annular portion comprising an upper mounting surface, such that the upper mounting surface may be removable affixed to the carrier head, a lower mating surface, an inside surface toward the center of the retaining ring between the lower mating surface and the upper mounting surface, an annular inset in the upper portion of the inside surface, an outside surface away from the center of the retaining ring between the lower mating surface and the upper mounting surface, and an annular inset in the upper portion of the outside surface; a second annular portion of a less rigid material than the first portion, the second portion comprising a lower wear surface, an upper mating surface, such that the upper mating surface engages the lower mating surface of the first rigid annular portion, an inside wall extending upwardly from the upper mating surface, the inside wall comprising an outside surface away from the center of the retaining ring, and a lip in the upper portion of the outside surface, such that the lip engages the annular inset in the upper portion of the inside surface of the first rigid annular portion, and an outside wall extending upwardly from the upper mating surface, the outside wall comprising an inside surface toward the center of the retaining ring, and a lip in the upper portion of the inside surface, such that the lip engages the annular inset in the upper portion of the outside surface of the first rigid annular portion.
 7. The retaining ring of claim 6 further comprising a beveled edge between the lower mating surface and the lower portion of the outside surface of the first rigid annular portion; and a beveled edge between the upper mating surface and the lower portion of the inside surface of the outside wall of the second annular portion.
 8. The retaining ring of claim 7 further comprising a beveled edge between the lower mating surface and the lower portion of the inside surface of the first rigid annular portion; and a beveled edge between the upper mating surface and the lower portion of the outside surface of the inside wall of the second annular portion.
 9. A method of assembling the second annular portion onto the first rigid annular portion, the method comprising providing a fixture comprising a top plate having a plurality of alignment holes, and a bottom plate having a plurality of dowel pins inserted into alignment holes, such that a spring is inserted over each dowel pin, the bottom plate including a recess for accepting the second annular portion of the retaining ring; placing the second annular portion in the recess of the bottom plate; positioning the first rigid annular portion over the second annular portion; placing the top plate over the dowel pins; and applying a downward force to the top plate, thereby driving the neck of the first rigid annular portion into the channel of the second annular portion.
 10. A method of removing the second annular portion from the first rigid annular portion, the method comprising inserting a plurality of screws into the mounting holes on the first rigid annular portion; alternately tightening the screws thereby forcing the second annular portion away from the first rigid annular portion. 